package com.ocom.common.utils;

/**
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 */
public class IdWorker {
    private final static Long twepoch = 1288834974657L;
    // 机器标识位数
    private final static Long workerIdBits = 5L;
    // 数据中心标识位数
    private final static Long datacenterIdBits = 5L;
    // 机器ID最大值
    private final static Long maxWorkerId = -1L ^ (-1L << workerIdBits);
    // 数据中心ID最大值
    private final static Long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    // 毫秒内自增位
    private final static Long sequenceBits = 12L;
    // 机器ID偏左移12位
    private final static Long workerIdShift = sequenceBits;
    // 数据中心ID左移17位
    private final static Long datacenterIdShift = sequenceBits + workerIdBits;
    // 时间毫秒左移22位
    private final static Long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    private final static Long sequenceMask = -1L ^ (-1L << sequenceBits);

    private static Long lastTimestamp = -1L;

    private Long sequence = 0L;
    private final Long workerId;
    private final Long datacenterId;

    public IdWorker(Long workerId, Long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException("worker Id can't be greater than %d or less than 0");
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException("datacenter Id can't be greater than %d or less than 0");
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized Long nextId() {
        Long timestamp = timeGen();
        if (timestamp < lastTimestamp) {
            try {
                throw new Exception("Clock moved backwards.  Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        if (lastTimestamp == timestamp) {
// 当前毫秒内，则+1
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
// 当前毫秒内计数满了，则等待下一秒
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = Long.valueOf(0);
        }
        lastTimestamp = timestamp;
// ID偏移组合生成最终的ID，并返回ID
        Long nextId = ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift) | sequence;

        return nextId;
    }

    private Long tilNextMillis(final Long lastTimestamp) {
        Long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private Long timeGen() {
        return System.currentTimeMillis();
    }
}
